Use local storage rather than cookies for persistence

[kingo55]

Cookies can be problematic with how much data is transmitted and processed by some web/application servers and we don't need Mojito cookies server-side.

Perhaps we should provide an option for localStorage or consider migrating all over to localStorage.

[dapperdrop]

@kingo55 would it make sense to approach it like #28? i.e. give users ability to customise persistence methods. We could make localStorage the new default and override to cookies in shared code as we migrate across?

[kingo55]

@dapperdrop - I think a config flag is most useful here.

Default to localStorage and have something like Mojito.options.useCookies = true; to toggle to cookies. Will be able to keep the cookie utilities functions for use in variant code then too.

[dapperdrop]

@kingo55 OK cool, that makes sense to me.

[kingo55]

We should think about this issue some more because it will impact #40 and we'll probably need a pathway to migrate old containers from cookies to local storage.

Of course if users are getting random numbers from a user seed/hash, then it shouldn't really matter, because they will get pretty much the same recipe unless they were excluded by sample during ramp up.